Successful technologies today seldom come about due to a grand “Eureka” event. Rather, they come from lots of people all having little Eurekas and little “damn, I was sure that would work” moments. -Clark Lindsey

Congratulations to SpaceX who landed the first stage intact.
Assuming cost is roughly related to stage mass and engine count, reusing the first stage saves 9/10 of the whole rocket cost.
If they can run the stage ten times, that means on average two new engines per flight as opposed to the original ten, meaning five fold savings.

Now there’s a few very interesting questions.

First is the amount of flights they can get per engine. First, I assume it’s going to be a low count, and experimental at that. Once they inspect and test the engines, they can improve them further.

Second is the ultimate development of the refurbishment process that has to be done to the vehicle between flights. If the turnaround takes a month and 200 people of three shifts each, then it doesn’t save much money, and might even be more expensive than just building a new stage.

If it requires one crane operator to drive some support tower there, place a new second stage, place a new payload, place fuel connections. After refueling they need some air traffic control type permission to fly again in a few hours. Then it has the potential to not only save a lot of money, but to place very large masses to orbit in a relatively short time.

I realize such a vision is still quite far off. Even if all the ground operations were somehow solved, just the winds frequently limit the launch and landing quite a lot at the moment.

Second stage

At the moment the second stage resembles the first one, only with one engine. However it is thrown away after use, as it’s hard to recover.

The first stage is easy to recover because it’s not yet very high or fast when it starts the return trip. On the other end of the stack, the Dragon capsule is relatively easy to recover since it’s so small, so you can make it really sturdy, put a lot of heat shield and parachutes (and RCS rockets on it), and it still doesn’t kill the total weight budget. You can also transport it over sea or land if need be.
One way to get around this would be to combine the second stage and the crew vehicle into one system. It is much more complicated to design though. We don’t want something as heavy as the Space Shuttle, and missions likely won’t need as much cross range anyway.

If a large portion of the flights are tanker flights, one might also not need a separate payload stage at all. Fit the second stage with RCS systems etc and transfer the propellant directly from its tanks. This could save costs a lot. The propellant depot would have most of the complexity, including the robot arm etc as it’s not being thrown away on every flight.

BFR – what do they need it for?

Elon Musk’s BFR plan is for about a 200 ton payload to low earth orbit, with 30 larger LOX-methane Raptor engines in the first stage. He plans to launch three, with two being refueling launches, so the Mars stack will be 600 tons upon leaving Earth orbit.

With Falcon 9 rockets and 10 t per flight, one would need 60 flights for a similar mass – surely hard to reach reliably and with a very long schedule – with last week’s technology!
But now, if the rocket can really be made to work reliably and simply in a Refuel And Go Again fashion, it seems feasible.
If, with some development, a single Falcon 9R flies once per week on average, it can place 500 tons per year to orbit, at relatively little cost. A fleet of twelve rockets might do it in a month! On the side, they would also have a myriad of other uses, revolutionizing spacefaring!

Also, if we can routinely get to Earth orbit relatively cheaply, we can start developing asteroid exploitation technology a lot sooner. Asteroids are the easiest source of materials in space since the delta vee and peak thrust needed to get to them and from them to basically anywhere in space is the lowest. I consider the small moons of Mars pretty much equivalent to asteroids in some senses too.
If you don’t need high peak thrust, you can do everything with high efficiency in space propulsion, and not rockets. Think ion engines or electrostatic sails or what ever. The only downside is the long flight time, but if the raw material hauling is done with robots anyway, I don’t see a problem with that. We just have to plan ahead. Sorry, Space Truckers!
Now, my vision is this:
– Falcon 9R and equivalents flying to low earth orbit frequently with little cost per flight, and
– propellants and raw materials brought from asteroids to Earth or Mars orbit or to the various Lagrange points, or even to cycling orbits (between Earth and Mars for example) with slow unmanned vehicles with high efficiency electric propulsion

With these you got yourself suddenly a potential for actually bringing humans to Mars in a relatively sustainable way.

Orbital Sciences crashed a rocket equipped with two 40 year old engines. Physically that old. They were an interim solution and they were working towards new engines. We don’t know at this point if the engines were to blame, but, to me, it is likely: engine brightening and thrust loss points to that. No people were hurt. In may this year, a similar NK-33 engine exploded in a test stand at NASA Stennis.

Last friday, Scaled Composites’ SpaceShipTwo disintegrated soon after its hybrid rocket engine was started. One of the two pilots was killed.

Many leaders had already quit the organization this year. Scaled had been critizised by some people in the industry for choosing a hybrid motor in the aircraft. Scaled Composites won the X Prize in 2004, ten years ago with the much smaller SpaceShipOne and a hybrid motor built by SpaceDev. The two flights to 100 km were successful. But scaling up to SpaceShipTwo size has taken unexpectedly long. They had a test stand explosion already in 2007, killing three people. The large amount of nitrous oxide (N2O) is dangerous as it is a monopropellant. A chain reaction can occur that will cause an explosion without any propellant mixing. The solid fuel part of the hybrid system can disintegrate and pieces of the solid can block the nozzle. Such things have happened with solid rockets, raising pressure and causing a runaway pressure rise and a catastrophic explosive failure.

I have not followerd Scaled Composites that closely, and I don’t know how many ground tests they have done. There has been talk that they were moving to a new fuel chemistry, but it is unclear if that was on this flight. SpaceshipTwo had already done some successful supersonic flights so the craft was not exploring new flight territory when it was destroyed.

To someone watching from afar, it might seem that failures would actually not be so hard to avoid. Could both of them have been avoided with a simple cure? Just 1) have more ground firings of the engine.

I’m in no position to say so myself for certain, but it seems like quite a simple.

No people were lost on the Orbital Antares flight. The payload was their own Cygnus unmanned space station resupply vehicle. So they can just rebuild the pad and fly again. With no lives at stake, it’s rational to go from engine tests to flight at a much earlier point.

With SpaceShipTwo the situation is much more severe. Two test pilots were flying the vehicle. The design was such that it required large amounts of pressurized monopropellant (N2O) and the engine chamber was large, containing large amounts of hot high pressure gas when operating.

In a liquid rocket engine, the risks can be mitigated a lot more easily since the chamber is a lot smaller than in a hybrid. The propellants (if ordinary ones are chosen) can not explode by themselves, and only a very small amount of them are mixed at any time in the preburners, pumps and chamber. So one way to avoid accidents like these is to 2) pick a fundamentally less dangerous approach.

There is even a third way to avoid accidents. Make the system resilient to individual component failures. Compared to Antares, in a SpaceX Falcon 9, would a single main engine giving up the ghost a few seconds into the flight resulted in a pad crash? If the stage would have stayed intact and the engine would not have exploded so violently that it would have destroyed other ones (if there were sensors for automatic engine shutdown), the mission would perhaps still have ended in failure but the pad might have been saved. If it had occurred later in flight, even the mission might have been salvageable.

And what about reusable vehicles, like SpaceShipTwo? Its design is like it’s made for tolerating engine problems: after the release in case of any trouble it can just glide to an easy landing, (possibly after venting the oxidizer). There’s no dangerous low altitude zone like with some ground launched vehicles. So the problem is just making really good sensors and having the engine stop at any sign of a problem. And of course making the engine stoppable. Hybrids are stoppable (compared to solids), but the amount of high pressure gas is still so big that it’s not straight forward to sense problems and control the system. The nitrous being a monopropellant can also cause issues.

So Scaled had a dream system. They built a great carrier aircraft, White Knight Two, which had similar avionics and cockpits and systems to SpaceshipTwo, and they test flew that a lot. They had carry and glide tests for SpaceshipTwo, made some changes and ironed out that part. They really knew how to do the aeroplane part, having built multiple record breaking craft before. What really is the tragedy here is that their propulsion seems to have too big failure modes – and just that one bit them now. So 3) Make the system always abortable.

This should apply to software business as well. You should have things like software component testing, regression, internal testing, customer testing. You should also have good software design like for example transactionality and constraints in databases. This stuff is also more than 40 years old, and if done right, categorically prevents a large amount of data corruption problems.

And then there’s the software development change management process which is another can of worms. I’ll write more about it in a couple of years…

Michael Alsbury was the SpaceshipTwo pilot who was killed in the accident. We should respect his memory and try to publicize ways to make space access safer for all. We should not say “space is hard”. We should say that space requires both a good comprehensive dedication as well as an open attitude towards safety.

“aerospike” in the first stage, though the individual bells are relatively large and few compared to some others. It might still work.

Their California office sits 100 meters from SpaceX, and Markusic is from SpaceX. Also, Scorpius which has built carbon rockets and pressure vessels is just a few blocks away.

They speak of smallish satellites, possible with modern tech. I’m slightly skeptical of the r strategy – but they sure are free to try. It might work well in this niche.

What are the fundamentals deciding which strategy is better – why are disposable gloves used for some cases, and reusable for some others?

Of course one could just compute the one-time, fixed and per-flight costs for each and find out some crossover points. But I feel there’s something more. So I don’t have a clear answer to this yet. The thinking has been going on for years.

Disclaimer, according to Wikipedia, the r/K selection theory of quantity vs quality offspring is already outdated.

These ram air kites by Skysails power flying in a figure eight circuit can develop power and also work as ship propulsion. Ideas like this have probably been toyed by many, it’s nice to see some execution. The biggest current product is 320 square meters and produces something equivalent to 2 MW of propulsion.

A flexible structure might be easy to store and the absolute lift is probably much more important than lift to drag at these low vessel speeds. I still wonder what high speed high aspect ratio glider style vehicles (tailed or tailles) could do in these applications. Control surfaces and all. Since lift is proportional to square of velocity.

And wouldn’t flying a circle or flattened ellipse or oval be more aerodynamically efficient with less tight turns and produce gentler load changes? Maybe there’s symmetry problems if you always go in a particular direction at higher altitude where the wind speed is higher. Or maybe the pull direction varies more.